1. Field of the Invention
In high-pressure fuel injectors, 3/2-way valves are used that include control slides, whose reciprocating motion influences the course of injection. The control slides execute reciprocating motions in the housing of a 3/2-way valve, and the seat faces and control edges of the control slide are exposed to severe stresses.
2. Prior Art
In 3/2-way valves, the control slides that enable the supply of fuel to the injection nozzle and block it are surrounded by a housing. The control slides and housing bores are made with the narrowest possible tolerances in terms of diameter, so as to achieve the most precise possible fuel metering and to keep leakage losses slight. The fuel metering is done via control edges on the outlet and inlet sides and is dependent on the stroke of the control slide in the housing of the 3/2-way valve. The mechanical stresses on the seat faces are very severe, since the motions of the control slide occur quite extensively undamped.
If the control slides in the 3/2-way valve housings execute only short reciprocating motions, then because of the short stroke travel only limited influence on the course of injection ensues. Since the course of fuel injection in an internal combustion engine, however, is highly significant for the course and completeness of combustion inside the cylinders, shaping of the injection course to optimize the course of combustion and for the sake of complete utilization of the internal energy of the fuel appears to be an indispensable method parameter that is dependent on the control stroke of the control valve member.
With the terminal-position damping, proposed according to the invention, of the control valve member inside the housing of the 3/2-way valve, the reciprocating motion in the terminal positions is damped in such a way that the service life of this component inside the 3/2-way valve housing increases considerably. As hydraulically acting dampers, diameter pairs offset from one another on the end regions of the control slide can be embodied, with which a pressure equilibrium can be generated in the chambers that surround the end regions of the control slide; as a result, the reciprocating motions of each control slide are damped. Thus the service life of the cylindrical element functioning as a control slide can be lengthened considerably. If the stop faces, opposite the end faces of the control slide, are embodied as flat annular faces, then on the one hand machining is simpler, and on the other, the wear resistance of a stop face embodied in this way is considerably higher, compared with a conical seat, for instance.
At the onset of injection, an actuator provided above the upper control chamber can be triggered, and as a result the pressure in the upper control chamber is lowered, which in turn moves the control slide to its upper terminal position. As a result, the inflow to the injection nozzle is opened and the injection nozzle is subjected to the fuel, which is at pressure.
The control valve member is preferably surrounded by a sleeve that is shrink-fitted into the housing of the 3/2-way valve and can thus easily be replaced if repair is necessary. The injector housing can be made from inexpensive material, while in this variant only the sleeve can be made from high-quality material. The control edges that result between the sleeve, shrink-fitted into the housing of the 3/2-way valve, and the shoulders of the control valve member, are made with close tolerances, so that minimal leakage ensues. By covering the control edges at the control valve member and at the shrink-fitted sleeve on the outlet and inlet side of the control valve member, minimal leakage losses are attainable, and the leakage can be returned to the fuel tank via a relief line.
Controlling the course of injection can be brought about by way of a stroke-dependent throttling, if the actuator above the upper control chamber is embodied as a piezoelectric actuator, for instance. A step can be made on the control valve member below the inlet-side control edge, and with this step an inlet-side throttling is attainable as a function of the stroke of the control valve member.